Telescopic shock absorber



Nov. 2

8 1'9444 c.-R. DOWN TELESCOPC SHOK ABSORBER YFiled Aug. 2. 1 943 'A 24 l u: www 25' Y 5ml4 Robert l 'maia-smi, i944 'rELnscoric snocx Asoanna Cyril Robert Down, Leamington Spa, England,

assignor to Automotive Products Company Limited, Leamington Spa, England Application August z, 1943, serial No. 497,088 Iii-Great Britain March 3o, 1942 1o claims. (ci. zer-c4) This invention relates to 'telescopic shock absorbers, and it has for its obje'ct to'provide an improved form and construction which is especially suitable for shock absorbers of theoleopneumatic type in which a workingv space of variable lvolume contains" a quantity of gas under pressure toprovide a resilient supporting means for the normalload ontheshock absorber, and

, a quantity of liquid, which latter is forced through one or more relatively constricted apertures as the volume of the working -space changes, thus damping the movements-of the shock absorber.

Inparticular the invention sets outtoprovide an exceptionally compact construction l of shock ,abSOrbig Strut forincorporation in the landing gear oi aircraft. l

In a telescopic shock absorber, havinga hollow plunger which contains damping liquid and is slidably mounted within-.one end of a cylinder, the present invention is characterised by the fact that said plunger is formed withva portion of rethrough the opposite end of the cylinder, the cyl'- in'der space surrounding the reduced portion of the plunger containing damping liquid and being means with connected through ilow restricting the interior of the plunger. L

As av furtherfeature of the invention there is provided a telescopic 'shock absorber comprising a cylinder, a stepped plunger having portions oi" large and small cross-sectional area slidable respectively through the ends of the cylinder, each in a fluid-tight manner, the cylinder 4space s urrounding the plunger being filled with damping liquid and being connected with-the interior of said plunger throughtlow restrictingmeans arvision of a telescopic shock absorber comprising in combination a cylinder, a hollow plunger extending axially Within the cylinder and projecting from -both'ends'thereof through huid-tight packing`devices, one end portion ofthe plunger. member being smaller in diameter than the other to form an annular variable volume space within l .the cylinder, damping liquid filling said annular space and `also partially iilling the plunger member, resilient means withinthe plunger member placing the liquid therein under pressure, and a damping valve in the plunger member forming'a constricted communication im'. dampingliquid between the interior ofthe plunger member and duced cross-sectional area extending slidably the variable volume cylinder space.

Preferably the plunger member comprises a pair of tubes of diierent-outside diameters arranged in axialalignment with their adjacent ends connected together and their outerends closed, the tubes of the plunger member con- .Veniently being connectedtogether by a collar which is secured to the outside of the smaller 'tube and to the inside of the larger tube. Flow restricting means operatively interposed between the damping liquid in the cylinder and the liquid within the plunger member 'conveniently comprises a damping valve member which is mountthe portion of larger cross-sectional area.

The invention is illustrated by Way of example in the accompanying diagrammatic drawing, in

ranged to bring about liquid .damping of the slid'- ii:1i g'movement of the plunger relative to the cylder. 1 j

vFurther, the improved .telescopic shock absorber may comprise a tubular cylinder, a stepped hollow plunger member slidable axially within r4'l-,liecylinder and projecting from both ends thereof. witha iluid-tight seal at one end of the cylinder slidably engaged by a larger diameter portion of the plunger member, and another uidtight seal at the opposite end of the cylinder slidably engaged by a smaller diameter portion of the plunger member, damping liquid within an annular cylinder space-surroundingr the plunger mem-r ber, and a damping valve device provided in the plunger member to produce arestricted communi-4 ber and the said annular cylinder space.

Thel invention further contemplates th'e pro- A cation between the interior of the plunger memwith a cylinder tube I2.

veniently grooved internally for v showing a modified arrangement.

which: Figure 1 is a sectional elevation through one form of shock absorbing strutincorporated in an aircraft undercarriage; and

Figure 2 is an elevation, partly in section,

In.-the embodiment shown in Figure 1 the undercarriage includes a fork member, one limb of which is indicated at I0, and is formed. with a substantially vertical `cylindrical bore II, lined The cylinder tube I2 is open at both ends. although the effective diameter at the upper end is reduced somewhat by the insertion of an annular plug I3 tted with a ltubular bush I4 composed of wear-resisting anti-frictional material. A second'tubular bush i5 is fitted at the lower end of the cylinder I2 andA isheld in position by a gland member I6, conthe accommodation oipacking rings I1.

A hollow plunger member,- indicated generally at I8, is arranged to' slide axially within the cylinder I2 and comprises a lower tubular portion I8, which is of relatively large diameter. connected rigidly at its upper end by a collar 20 with volume of the cylinder space 35 owing to thel stepped" construction of said plunger member. Therefore, damping liquid is ejected from the cylinder space 35 and flows relatively freely through the passage or passages 34 into the compartment 3| of the plunger member. The entering liquid forces down the oating piston 26 and .consequently increases the compression of the air with..

being closed by a plug 24, which is bored at 25 to receive the usual axle (not shown) of the landing wheel.

A floating piston 28, having a packing ring 21, is freely slidable within the lower tubular portion I8 and is fitted with an upwardly extending tubular stem 28 sealed near its upper end by a disk 29 welded or otherwise secured within the bore of the stem. 'I'he upper extremity of the stem 28 is formed with large perforations, and is flared to form a guide 30, which is freely slidable without undue looseness within the upper tubular portion 2| of the plunger member I8. Thus the floating piston 26serves to divide the interior of the plunger member I8 into two separate compartments, which are indicated at 3| and 32 respectively, the compartment 3| including the whole of the plunger space disposed outside the stem 28, while the compartment 32 includes the space within the stem 28 as far up as the disk 28, An air inlet valve, indicated at 33, is provided to enable compressed air to be pumped into the compartment 32. The compartment 3| is completely filled with damping liquid, which latter extends through one or more passages 34 formed' in the collar 20, to the annular space 35, which is herein termed the cylinder space. The requisite quantity of damping liquid is inserted through a passage 36-having a closure plug 31, the shock absorber sually being charged withliquid before the air is pumped into the compartment 82.'

A damping valve is provided in commotion with the passage or passages 34', said valve convenient comprising an annular valve member 38, whic is arranged to slide upon the lower end of the tubular portion 2 I, its'movement, being limited by a stop flange 39. The upper surface of the valve member 38 is provided with a circular groove' and from the bottom of this one or more relatively small damping passages 40 lead into the compartment 3| Thus,whenthe liquid pressure in the cylinder space 35 is greater than that in the compartment 3| the damping liquid can flow relatively freely through the passage or passages '34 and'then past the outside of the valve member.

38 to the compartment 3|. On the other hand,

when liquid tends to flow in the `opposite direcquite wellknown in the art.

InV order to limit the stroke of the plunger part'of the annular plug I3 for limiting the downi ward movement, while upward movement is similarly restricted bythe engagement of the shoul- When the aircraft lands, or encounters a bump during taxying, the plunger member I8 is forced V8 5 member Il it is formed at its upper end with a- -flange 4| adapted to co-operate with the upper '70'- der 42 of the plunger member 'I8 with the under- Anea'th surface of said annular plug I3. f l

` upward1y which has the effect of reducing the u escape through the damping passages 48 back into the cylinder space 35. The quantity of liquid displaced from the cylinder space 35 during upward movement of the plunger member I8 is, of course, dependent uponv the difference in the cross-sectional areas of the larger portion i9 ci the plunger member and the smaller portion ti thereof; as this effective area can be made relatively small, the shock absorber can readily be arranged so that only a small movement oi the floating piston 26 is brought about by the full stroke of the shock absorber.' Therefore the Variation in pressure within the compartment 32 is correspondingly small and a high air pressure can satisfactorily be used, thus enabling a relatively compact shock absorber to be designed. The fact that the interior of the stem 28 forms part of the air compartment 32 also assists in this connection. y

A somewhat modified construction of shock absorbing strut is shown diagrammatically in Figure 2, similar but not identical parts being indicated by use of the same numerals together with the suilix a". In general arrangement it resembles that shown in ,Figure 1 but the collar 20a is extended radially to :form a piston 43 which slides in a liquid-tight manner within the cylinder i2a owing to the provision o f a packing ring it; the piston consequently divides the cylinder space into two separate portions, namely a main cylinder space 35a and an annular recoil damping chamber 45. It will be noted that in order that the recoil damping chamber 45 may have a suf'licient cross-sectional area the lower tube |9a of the .plunger member I8a is arranged to be substan- -tially smaller than the cylinder tube I2a. 'The -of passages "affording communication between the main cylinder space 35a and the recoil damping chamber 45, said passages, however, being controlled by an annular damping valve member 48 similar in construction to the valve member dit in Figure 1.

During upward movement of the plunger member I8a some of the liquid fromthe main cylinder space 35g flows through the passages 41 into the .recoil damping chamber=45, the now being fairly free so that the upward movement is not substantially affected. At the same ltime the remainder of the liquid ejected from the main cylinder space 35a flows through the passages 34a into the plunger member Ila and pressing down 4. A telescopic shock absorber as claimed in the floating piston 26d increases the pressure of claim 2, wherein the plunger member comprises the air in the compartment 32a. f, a pair of tubes of dinerent outside diameters ar- When the downward or recoil stroke of the ranged in axial alignment with their adjacent plunger member lea commences, the,damping .6 ends connected together and their outer ends liquid, in trying to flow'from the recoil damping closed. the tubes of the plunger member being chamber 45 back to the main cylinder space 35a, connected together by a collar which is secured lifts the damping valve 48-to its closed posiv to the outside of the smaller tube and to the intion, in which the liquid is constrained to ilow side of the larger tube. through one or more very small openings in the l 5. A shock absorber as claimed in claim 2, valve member 48.' Therefore. downward movewherein the damping valve is mounted upon the ment of the plunger member isa Iis positively plunger member at the position where the pordamped by the liquid which is trapped in the retion of smaller cross-sectional area joins the porcoil damping chamber 45 and at the same time tion of larger cross-sectional area.

there is no danger of a partial vacuum being l 6. A chock absorber as claimed in claim 2, vformed in the-main cylinder space a as liquid wherein the resilient means within the plunger can return relatively freely to that space from member is a quantity of compressed gas, and a the compartment 3Ia. f floating piston is arranged to separate the damp- It will be understood'that the preferred coning liquid in the plunger member from the comstructions -are capableof many modifications in 20 .pressed gas, the floating piston being slidably ordento suit particular requirements. For inmounted in that portion of the plunger member l stance-the shock absorbing strut can be arranged having the larger cross-sectional area.

to operate in any desired position, as the damping 7. A shock absorber -as claimed in claim 2, liquid and compressed air are eiilciently separated wherein the resilient fmeans within the plunger by the floating piston. The 'damping valve device 25 member is a quantity of compressed gas, and a may, of course, take various forms and it can be iloating piston is arranged to separate the dampincorporated, if desired, in the wall of the upper ing liquid in the-plunger member from the comor lower part of the plunger member. It will Dressed gee. the fleeting Piston being Slidebly be observed that, ,in the construction shown in mounted in that portion of the plunger member Figure 1, the only 'tube surfaces which require to 30 having the larger cross-sectional area and being be finely finished in order to produce emcient Provided with en axial Stem Which engages Slidsliding are the external surfaces of the upper and' ably with the interior of the smaller cross-seclower parts of the plunger member andthe intional pertion of the plunger member, thus reternal surfaceof the lower part thereof. In some taining the floating Pisten Substantially in true cases it may be possible to produce the plunger 3" alignment with the plunger member. Tmemberfrom a singlelength vof tubing which 8- A Sheek absorber las claimed in claim 2,y is rolled or otherwise treated so` that its twg end wherein the resilient means 'within the plunger portions are of the requisite different diameters. member iS e quentlty 0f compressed ges. ende What I claim isn iloating piston is arranged to separate the damp-.- 1. A telescopic shock absorber having a hollow i118 liquid in the plunger member frein the eemplunger which contains damping liquid and is PreSSed 88S, the lloetlng pieton being .slidably slidably mounted within one end of la cylinder; mounted 111 that Portion 0f the plunger member wherein said plungerl is fonned with a portion or having e larger cross-Seetional aree and being reduced vcross-sectional area extending slidably Prelude with en aXiel Stern which engages slidthrough the opposite end of the cylinder to form 5 ably with e interior of the smaller cross-seca cylinder spnoe openingonly to the melde of tional port on of the plunger member, thus rethe plunger, the cylinder epee-ev surrounding the t taining the floating piston substantially in truereduced portion of the plunger containing dempalignment with' the plunger member. the stem ing'liquid and being connected through flow lre.. portion of the floating piston being hollow and stricture' means witn'tlie interior ofthe plunger, 5 having its interior infree communication with andmeans for maintaining pressure on the liquid. the compressed 88S Spce 2. A telescopic shock absorben eomprlslng m 9. A shock absorbermsA claimed in claim 2, combination e ey'llnder, e hollow plunger extendwherein the larger cross-sectional portion of the ing axially within the cylinder and projeetlng plunger member is smaller than the interior of Y. from both end, thereoflhmugh ultlghtmk, 55. the Vcylinder and a piston flange -formed u pony ing devices, one end portion-of the-plungermem the plunger member engages Slidebly with the ber being smaller in diameter theutne other to interior 0f the cylinder. thereby dividing ithe enforman annular, variable volume space within `nular cylinder space into a main cylinder space thee under, dam ln ll uldi and a recoil damping chamber.

speceyend al lalgly glllgmtlglsngengl 10. A shock absorber. as claimed in claim 2, ber, resilient means within the plunger member wherein the larger cross-sectional portion of the plnelng the llquld therein 'under pressure and plunger member is smaller than' the interior of a damping valve in the plunger member fel-mms the cylinder and a piston ilange formed upon the a constricted communication for damping liquid plunger member engages lldably' with the m' now between the ulterior of the plunger member 5 terior of the cylinder, thereby dividing the anclaim-2, wnereln the plunger member comprises :beting als a resigrictd communication between Sentir. of tubes of diil'erent outside diameters 7o e re dam? g c amber-end the main eyllnarranged in axial alignment with their ediacent der space.

el um together and their outer ends CYRILA Roemer Down. 

